I was shooting video at an open air set for a local band today. While I was tucked in behind the drummer to try to get some interesting shots, I noticed that the bass actually sounded better coming from the back of the bass cab than it did from the front. So, has anybody miked the back of a cab for recording purposes? Can this be done? I know there a phase issues with doing this.. but it seemed that the forward projection of sound was not interfering with the rearward "live". What would happen during recording do you think?

My experience has been that you place a mic on a cabinet where ever it sounds best.  Getting down at speaker level is the best place to really hear what is coming out of them.  If I was going to mic the back of the cabinet to capture bass that I thought sounded good, I would still mic the front as well with a second mic to make sure I got the highs coming out of the speaker, then blend them to taste.  

The rear panel of a bass cab can could be acting as a sort of vibrating surface creating sound from behind. (A well braced design should be quieter back there!)  On the odd occasion I have miced up a bass cab from behind it produced more of a sub type sound with the depth there, not much detail as Makeshift is suggesting. You would still need either the DI sound or the sound from the front too combined. It would not be a great sound on its own. 

You would have to check your phasing options in this type of situation as well just to be sure. 
 
An upright piano sounds nice from the back too and the detail is still there in the sound as well which is sort of nice. But even with a piano I would still take the front cover off and put a mic pointing at the strings and hammers for a little more detailed information.

for live work, the Palmer PDI-09 is a much more elegant answer...

for basses, a good direct box will always beat out a mic, for clarity, eq, punch and control.

Thanks for the feedback guys. Thinking about it some more I am now thinking what I heard was probably specific to that setup... there was a brick wall not 10 feet behind the cab... it was probably an effect of that particular setup in that particular spot in that particular venue.